Crash with supercall to Java interface

[lrytz]

Related to #143 - possibly regressed in scala/scala#5377 (just a guess):

T.java

interface T { default int f() { return 1; } }

Test.scala

trait U extends T
class C extends U { def t = super.f }

compiling scalac Test.scala T.java

java.lang.AssertionError: assertion failed:
  cannot invokespecial T.f, the interface is not a direct parent.

For some reason we don't catch this case in SuperAccessors.

[lrytz]

Fixed in my branch for #228 that eliminates static forwarders (https://github.com/scala/scala/compare/2.12.0...lrytz:traitSuperAccessors?expand=1)

[adriaanm]

scala/scala#5429